6 ms·

The King of Human Error

92 points by gruseom 15y ago

joshu 15y ago
a while ago I did a mechanical turk experiment that shows experimentally a bit of how kahneman/tversky prospect theory ends up working: http://joshua.schachter.org/2008/09/amateur-economist.html http://joshua.schachter.org/2008/09/amateur-economist.html
crntaylor 15y ago
The quiz that accompanies this article [1] makes an error. Question 2 asks "A team of psychologists performed personality tests on 100 professionals, of which 30 were engineers and 70 were lawyers. Brief descriptions were written for each subject. The following is a sample of one of the resulting descriptions: Jack is a 45-year-old man. He is married and has four children. He is generally conservative, careful, and ambitious. He shows no interest in political and social issues and spends most of his free time on his many hobbies, which include home carpentry, sailing, and mathematics. What is the probability that Jack is one of the 30 engineers?" The answer given is that the probability is exactly 30%, since there are 30 engineers out of 100. But this ignores all of the information available in the description! Imagine if the description said "Jack's hobbies include writing compilers, hacking assembly code, World of Warcraft, designing new programming languages and LARP." Would we still conclude that there's only a 30% chance of him being an engineer? A correct answer to this question should apply Bayes' rule. With E representing 'Jack is an engineer', L representing 'Jack is a lawyer' and D representing the description, Bayes rule tells us P(E|D) = P(E) P(D|E) / P(D) P(L|D) = P(L) P(D|L) / P(D) where P(A|B) is 'the probability of A given B' and P(A) is 'the probability of A without taking other information into account'. We can ignore the common factor of 1/P(D) and we know that P(E)=0.3 and P(L)=0.7, so the relative probabilities of Jack being an engineer or a lawyer, given the description of him, are P(E|D) ~ 0.3 * P(D|E) P(L|D) ~ 0.7 * P(D|L) so the a priori probabilities of Jack being an engineer or a lawyer need to be weighted by the probability of seeing the description that we did, given that Jack is an engineer or a lawyer! If you claim that there is a 70% chance of seeing the description if Jack is an engineer but only 30% if Jack is a lawyer, then taking all the evidence into account, you should ascribe an equal probability to the two possibilities. Basic probability fail by the editors of Vanity Fair, I think. [1] http://www.vanityfair.com/business/features/2011/12/kahneman-quiz-201112 http://www.vanityfair.com/business/features/2011/12/kahneman...
- ckuehne 15y ago
  Not only do they seem to lack basic probability skills. They also cannot cite the original material correctly. Kahneman and Tversky tested something else completely. Namely, that people tend to ignore base rates when making probability estimates. From Kahneman's book: "In one experimental condition, subjects were told that the group from which the descriptions had been drawn consisted of 70 engineers and 30 lawyers. In another condition subjects were told that the group consisted of 30 engineers and 70 lawyerss. [..] In sharp violation of Bayes' rule, the subjects in the two conditions produced essentially the same probability judgements." There is also a blatant error in the OP article: Answer No. 2 (Linda is a bank teller and is active in the feminist movement.) is by no means "logically impossible". EDIT: wording
  - three14 15y ago
    'There is also a blatant error in the OP article: Answer No. 2 (Linda is a bank teller and is active in the feminist movement.) is by no means "logically impossible".' They meant that it's logically impossible for the probability of A AND B to be higher than the probability of A, since A AND B is a subset of A. She could be feminist, but the probability of being feminist is lower than the 100% probability that she's either a feminist or not.
    - ckuehne 15y ago
      I am well aware of the point they were trying to make. Or, more precisely, the point Kahneman et al. were trying to make. What I am concerned about is that they, that is, the editors / writers of Vanity Fair, do not understand their mistake. This is somewhat likely given the error they made described by the grandparent comment. Overall, I find it rather ironic to find such gross errors in an article that sets out to educate the reader about "human error".
    - bluedanieru 15y ago
      I'm going to copy/paste the relevant section: Then they went around asking people the same question: Which alternative is more probable? (1) Linda is a bank teller. (2) Linda is a bank teller and is active in the feminist movement. The vast majority—roughly 85 percent—of the people they asked opted for No. 2, even though No. 2 is logically impossible. (If No. 2 is true, so is No. 1.) They say: "If No. 2 is true, so is No. 1.", but they omit that the opposite does not hold. Perhaps they thought it was obvious enough. I think they get it and just left that second part out. They may have worded it poorly (better would be "it is logically impossible that #2 could be the correct answer"), but it was very clear to me when reading the article that the editors meant exactly what you describe.
mturmon 15y ago
A well-written (by Michael Lewis) article that should invite people interested in economics and human or rational decision-making to get to know Kahneman's work, which won the Nobel prize, better. Engineers try to make rational decisions but probably we don't realize the extent to which it's not really human nature to do so. Teaser: Amos [Tversky] and I once rigged a wheel of fortune. It was marked from 0 to 100, but we had it built so that it would stop only at 10 or 65 One of us would stand in front of a small group, spin the wheel, and ask them to write down the number on which the wheel stopped, which of course was either 10 or 65. We then asked them two questions: Is the percentage of African nations among UN members larger or smaller than the number you just wrote? What is your best guess of the percentage of African nations in the UN? The spin of a wheel of fortune had nothing to do with the question and should have had no influence over the answer, but it did. “The average estimate of those who saw 10 and 65 were 25% and 45 respectively.”
- SkyMarshal 15y ago
  I wonder what the control group/s who was/were asked the questions without the wheel came up with.
  - jonsen 15y ago
    Aren't the emerging two groups each others control group? What could you gain from your proposed control experiment?
    - cdog46 15y ago
      That article, as written in Vanity Fair, is so poorly written. Paragraph one is evidence enough. More indefinite modifiers so that you don't know who is who. Also I don't understand why answer 1 is the correct answer regarding Linda. There is simply not enough information given to determine which answer is true.
      - andrenotgiant 15y ago
        Regarding the Linda the Bank Teller Question: Here is an analogous numbers only probability question: You are told that the test administrator is thinking of a number between 1 and 100, and that the number is odd. What is more likely? A. The number is greater than 50. B. The number is greater than 50 and ends with a 3, 5, 7 or 9 Answer A and you have a 50% chance of being correct. Answer B and you only have a 40% chance of being correct.
JoeAltmaier 15y ago
"They had a rule of thumb, he explains: they would study no specific example of human idiocy or irrationality unless they first detected it in themselves." God I love these guys.
- danielharan 15y ago
  Also love this passage: “Most people after they win the Nobel Prize just want to go play golf,” said Eldar Shafir, a professor of psychology at Princeton and a disciple of Amos Tversky’s. “Danny’s busy trying to disprove his own theories that led to the prize. It’s beautiful, really.” It shows amazing intellectual honesty.
dombercz 15y ago
cliffs?
kstenerud 15y ago
"Which alternative is more probable? (1) Linda is a bank teller. (2) Linda is a bank teller and is active in the feminist movement. The vast majority—roughly 85 percent—of the people they asked opted for No. 2, even though No. 2 is logically impossible. (If No. 2 is true, so is No. 1.) The human mind is so wedded to stereotypes and so distracted by vivid descriptions that it will seize upon them, even when they defy logic, rather than upon truly relevant facts." Umm.. no. The reason 85% of people chose option #2 is because the answers were so poorly worded. They give the impression of an unspoken assumption for answer #1 that Linda is NOT active in the feminist movement.
- luu 15y ago
  That's not the reason. The question seems clear to me. Moreover, your assertion could only be true if people believed that more than half of female bank tellers are involved in the feminist movement, which is implausible.
  - kstenerud 15y ago
    The question most certainly did not seem clear to me. And the assertion does not require more than half of female bank tellers to be involved in the feminist movement. Rather, bank teller becomes an irrelevant side-fact, and the focus of discussion becomes whether Linda is more likely to be part of the feminist movement given her being deeply concerned with issues of discrimination and social justice. Human language is imprecise, and comes with assumptions based on context and culture. The people who came up with this question succumbed to the false assumption that the majority of people would interpret the wording of the question the same way they did. Because of the flawed nature of the question an the incorrect assumptions of the test givers, this question cannot be relied upon to give any measure of the "conjunction fallacy".
- vilhelm_s 15y ago
  Various alternative explanations like that have been explored, but it seems the effect is not due to wording: http://lesswrong.com/lw/jj/conjunction_controversy_or_how_they_nail_it_down/ http://lesswrong.com/lw/jj/conjunction_controversy_or_how_th...
boas 15y ago
> Which alternative is more probable? > (1) Linda is a bank teller. > (2) Linda is a bank teller and is active in the feminist movement. If Linda is a randomly chosen person, then clearly 1 is more probable. However, there is another sense in which 2 is more likely to be true. For example, in the radiology department where I work, doctors ordering studies need to enter in a reason for the study. Frequently, they put something generic like "pain" to get the study approved, which may or may not be accurate. On the other hand, if I saw a history that said "1 day history of RLQ pain, nausea, and fever", I would consider that history to be more likely to be true. So in a narrow probabilistic sense, 1 is true, but when you consider that people sometimes make stuff up or don't have the full story, you might rationally judge a more detailed story to be more believable.
SteveSailer 15y ago
The Vanity Fair staffer, Jaime Lalinde, who made up the sidebar quiz, misinterpreted Kahneman's point through the lens of political correctness: Stereotypes (even about engineers) Are Wrong!

92 points by gruseom 15y ago

joshu 15y ago

a while ago I did a mechanical turk experiment that shows experimentally a bit of how kahneman/tversky prospect theory ends up working: http://joshua.schachter.org/2008/09/amateur-economist.html http://joshua.schachter.org/2008/09/amateur-economist.html

crntaylor 15y ago

The quiz that accompanies this article [1] makes an error. Question 2 asks "A team of psychologists performed personality tests on 100 professionals, of which 30 were engineers and 70 were lawyers. Brief descriptions were written for each subject. The following is a sample of one of the resulting descriptions: Jack is a 45-year-old man. He is married and has four children. He is generally conservative, careful, and ambitious. He shows no interest in political and social issues and spends most of his free time on his many hobbies, which include home carpentry, sailing, and mathematics. What is the probability that Jack is one of the 30 engineers?" The answer given is that the probability is exactly 30%, since there are 30 engineers out of 100. But this ignores all of the information available in the description! Imagine if the description said "Jack's hobbies include writing compilers, hacking assembly code, World of Warcraft, designing new programming languages and LARP." Would we still conclude that there's only a 30% chance of him being an engineer? A correct answer to this question should apply Bayes' rule. With E representing 'Jack is an engineer', L representing 'Jack is a lawyer' and D representing the description, Bayes rule tells us P(E|D) = P(E) P(D|E) / P(D) P(L|D) = P(L) P(D|L) / P(D) where P(A|B) is 'the probability of A given B' and P(A) is 'the probability of A without taking other information into account'. We can ignore the common factor of 1/P(D) and we know that P(E)=0.3 and P(L)=0.7, so the relative probabilities of Jack being an engineer or a lawyer, given the description of him, are P(E|D) ~ 0.3 * P(D|E) P(L|D) ~ 0.7 * P(D|L) so the a priori probabilities of Jack being an engineer or a lawyer need to be weighted by the probability of seeing the description that we did, given that Jack is an engineer or a lawyer! If you claim that there is a 70% chance of seeing the description if Jack is an engineer but only 30% if Jack is a lawyer, then taking all the evidence into account, you should ascribe an equal probability to the two possibilities. Basic probability fail by the editors of Vanity Fair, I think. [1] http://www.vanityfair.com/business/features/2011/12/kahneman-quiz-201112 http://www.vanityfair.com/business/features/2011/12/kahneman...

ckuehne 15y ago
Not only do they seem to lack basic probability skills. They also cannot cite the original material correctly. Kahneman and Tversky tested something else completely. Namely, that people tend to ignore base rates when making probability estimates. From Kahneman's book: "In one experimental condition, subjects were told that the group from which the descriptions had been drawn consisted of 70 engineers and 30 lawyers. In another condition subjects were told that the group consisted of 30 engineers and 70 lawyerss. [..] In sharp violation of Bayes' rule, the subjects in the two conditions produced essentially the same probability judgements." There is also a blatant error in the OP article: Answer No. 2 (Linda is a bank teller and is active in the feminist movement.) is by no means "logically impossible". EDIT: wording
- three14 15y ago
  'There is also a blatant error in the OP article: Answer No. 2 (Linda is a bank teller and is active in the feminist movement.) is by no means "logically impossible".' They meant that it's logically impossible for the probability of A AND B to be higher than the probability of A, since A AND B is a subset of A. She could be feminist, but the probability of being feminist is lower than the 100% probability that she's either a feminist or not.
  - ckuehne 15y ago
    I am well aware of the point they were trying to make. Or, more precisely, the point Kahneman et al. were trying to make. What I am concerned about is that they, that is, the editors / writers of Vanity Fair, do not understand their mistake. This is somewhat likely given the error they made described by the grandparent comment. Overall, I find it rather ironic to find such gross errors in an article that sets out to educate the reader about "human error".
  - bluedanieru 15y ago
    I'm going to copy/paste the relevant section: Then they went around asking people the same question: Which alternative is more probable? (1) Linda is a bank teller. (2) Linda is a bank teller and is active in the feminist movement. The vast majority—roughly 85 percent—of the people they asked opted for No. 2, even though No. 2 is logically impossible. (If No. 2 is true, so is No. 1.) They say: "If No. 2 is true, so is No. 1.", but they omit that the opposite does not hold. Perhaps they thought it was obvious enough. I think they get it and just left that second part out. They may have worded it poorly (better would be "it is logically impossible that #2 could be the correct answer"), but it was very clear to me when reading the article that the editors meant exactly what you describe.

mturmon 15y ago

A well-written (by Michael Lewis) article that should invite people interested in economics and human or rational decision-making to get to know Kahneman's work, which won the Nobel prize, better. Engineers try to make rational decisions but probably we don't realize the extent to which it's not really human nature to do so. Teaser: Amos [Tversky] and I once rigged a wheel of fortune. It was marked from 0 to 100, but we had it built so that it would stop only at 10 or 65 One of us would stand in front of a small group, spin the wheel, and ask them to write down the number on which the wheel stopped, which of course was either 10 or 65. We then asked them two questions: Is the percentage of African nations among UN members larger or smaller than the number you just wrote? What is your best guess of the percentage of African nations in the UN? The spin of a wheel of fortune had nothing to do with the question and should have had no influence over the answer, but it did. “The average estimate of those who saw 10 and 65 were 25% and 45 respectively.”

SkyMarshal 15y ago
I wonder what the control group/s who was/were asked the questions without the wheel came up with.
- jonsen 15y ago
  Aren't the emerging two groups each others control group? What could you gain from your proposed control experiment?
  - cdog46 15y ago
    That article, as written in Vanity Fair, is so poorly written. Paragraph one is evidence enough. More indefinite modifiers so that you don't know who is who. Also I don't understand why answer 1 is the correct answer regarding Linda. There is simply not enough information given to determine which answer is true.
    - andrenotgiant 15y ago
      Regarding the Linda the Bank Teller Question: Here is an analogous numbers only probability question: You are told that the test administrator is thinking of a number between 1 and 100, and that the number is odd. What is more likely? A. The number is greater than 50. B. The number is greater than 50 and ends with a 3, 5, 7 or 9 Answer A and you have a 50% chance of being correct. Answer B and you only have a 40% chance of being correct.

JoeAltmaier 15y ago

"They had a rule of thumb, he explains: they would study no specific example of human idiocy or irrationality unless they first detected it in themselves." God I love these guys.

danielharan 15y ago
Also love this passage: “Most people after they win the Nobel Prize just want to go play golf,” said Eldar Shafir, a professor of psychology at Princeton and a disciple of Amos Tversky’s. “Danny’s busy trying to disprove his own theories that led to the prize. It’s beautiful, really.” It shows amazing intellectual honesty.

dombercz 15y ago

cliffs?

kstenerud 15y ago

"Which alternative is more probable? (1) Linda is a bank teller. (2) Linda is a bank teller and is active in the feminist movement. The vast majority—roughly 85 percent—of the people they asked opted for No. 2, even though No. 2 is logically impossible. (If No. 2 is true, so is No. 1.) The human mind is so wedded to stereotypes and so distracted by vivid descriptions that it will seize upon them, even when they defy logic, rather than upon truly relevant facts." Umm.. no. The reason 85% of people chose option #2 is because the answers were so poorly worded. They give the impression of an unspoken assumption for answer #1 that Linda is NOT active in the feminist movement.

luu 15y ago
That's not the reason. The question seems clear to me. Moreover, your assertion could only be true if people believed that more than half of female bank tellers are involved in the feminist movement, which is implausible.
- kstenerud 15y ago
  The question most certainly did not seem clear to me. And the assertion does not require more than half of female bank tellers to be involved in the feminist movement. Rather, bank teller becomes an irrelevant side-fact, and the focus of discussion becomes whether Linda is more likely to be part of the feminist movement given her being deeply concerned with issues of discrimination and social justice. Human language is imprecise, and comes with assumptions based on context and culture. The people who came up with this question succumbed to the false assumption that the majority of people would interpret the wording of the question the same way they did. Because of the flawed nature of the question an the incorrect assumptions of the test givers, this question cannot be relied upon to give any measure of the "conjunction fallacy".
vilhelm_s 15y ago
Various alternative explanations like that have been explored, but it seems the effect is not due to wording: http://lesswrong.com/lw/jj/conjunction_controversy_or_how_they_nail_it_down/ http://lesswrong.com/lw/jj/conjunction_controversy_or_how_th...

boas 15y ago

> Which alternative is more probable? > (1) Linda is a bank teller. > (2) Linda is a bank teller and is active in the feminist movement. If Linda is a randomly chosen person, then clearly 1 is more probable. However, there is another sense in which 2 is more likely to be true. For example, in the radiology department where I work, doctors ordering studies need to enter in a reason for the study. Frequently, they put something generic like "pain" to get the study approved, which may or may not be accurate. On the other hand, if I saw a history that said "1 day history of RLQ pain, nausea, and fever", I would consider that history to be more likely to be true. So in a narrow probabilistic sense, 1 is true, but when you consider that people sometimes make stuff up or don't have the full story, you might rationally judge a more detailed story to be more believable.

SteveSailer 15y ago

The Vanity Fair staffer, Jaime Lalinde, who made up the sidebar quiz, misinterpreted Kahneman's point through the lens of political correctness: Stereotypes (even about engineers) Are Wrong!